Piston for internal combustion engines



Jan. 3, 1956 D. VON LASSBERG ETI'AL 2,729,523 PISTON FOR INTERNALCOMBUSTION ENGINES Filed March 8, 1952 INVENTORS DlETmm-a vow mssmma 15K8, FRANZ GEBHART ATTORNEYS United States Patent PISTON FOR INTERNALCOMBUSTION ENGINES Dietrich von Lassberg and Franz Gebhart, Augsburg,Germany, assignors to Maschinenfabrik Augsburg- Niirnberg A. G.,Augsburg, Germany, a corporation of Germany Application March 8, 1952,Serial No. 275,572

Claims priority, application Germany March 15, 1951 3 Claims. (Cl.30917) This invention relates to a piston for internal combustionengines, more particularly, diesel engines, of the crosshead type.

The conventional crosshead type diesel engines which are always oflarger dimensions, have steel or cast iron pistons. Such engines arealmost exclusively provided with pistons which are cooled with water oroil. This, of course, requires a considerable expenditure of means forsupplying and discharging the cooling agent and for re-cooling the same,whereby the engine of course becomes complicated and liable todisturbances.

It is the object of the present invention to provide a construction bywhich these disadvantages are avoided.

With this and further objects in view, according to the presentinvention a piston body of light metal is used which is connected to apiston rod of steel. Light metal pistons are already used in smallerinternal combustion engines without crosshead, but the opinion has beengenerally accepted that with larger internal combustion engines,especially of the crosshead type, it is absolutely necessary to providea cooled piston. Although it was realized that with light metal pistonsowing to their better heat conductibility more heat is trans mitted fromthe combustion chamber into the cylinder wall, substantial difiicultieswere caused in regard to the connection between the piston and thepiston rod, since the piston rod of steel has a smaller coefiicient ofthermal, expansion than the attached light metal piston and reacheslower temperatures in operation than the piston.

In the conventional mode of fastening the piston rod to the lower end ofthe piston of a crosshead type diesel engine, the piston under action ofhigher temperatures is liable to a larger thermal expansion between thefixing screws than over the rest of its outer surface, whereby thebearing length of the piston may become oval and bear non-uniformly inoperation. This will be particularly true in light metal pistons oflarger di mensions.

Therefore, according to a further important feature of the invention thefixing flange is arranged at apart of the piston whose diameter issmaller than the maximum diameter of the bearing length of the piston,i. e. in a region where the piston owing to its taper does not bear onthe cylinder liner, so that detrimental efiects owing to ovalization ofthe piston at the point of its connection with the piston rod areavoided. 0f course, it is not necessary for the piston to be conicallyshaped at the point where the piston rod is connected to the piston,provided only that the respective portion of the piston is smaller indiameter than the maximum diameter of the piston so that the same isprevented from engaging the cylinder liner as a result of a deformationcaused by the non-uniform thermal expansion of piston and piston rod.Moreover, the piston has a substantially higher stiifness in this regionthan at its bearing end so that it cannot so easily follow its tendencyof ovalization as it would be the case in the relatively thinwalled partforming the bearing length of the piston.

2,729,523 Patented Jan. 3, 19 56 In the drawing,

Fig. l is an axial section through a piston embodying this invention;and

Fig. 2 is a diagrammatic showing in section of an engine having a pistonembodying this invention and used with a crosshead.

In the drawing, the piston 3 is fastened on its piston rod l with theaid of several threaded bolts 2 which are made longer and thinner thannormally necessary so as to permit a considerable elongation thereofunder tension, as is known per se. Threaded sleeves 5 of steel areembedded in the light metal piston body 3 to provide a reliableanchoring of the screws 2 in the female thread of the piston, andspacing sleeves 6 are inserted between the flange 7 of the piston rod 1and the nuts 8 of the threaded bolts 2. The transverse plane ofconnection 4 between the piston rod 1 and the piston body 3 is locatedin the annular zone which has a smaller diameter than the cylindricalpart a of the piston body 3. The piston body 3 may be conical over thelength b or it may be cylindrical for the major part thereof, with ashort transitional portion between the maximum diameter of the bearinglength a and the reduced diameter of the part b which does not bear onthe cylinder liner. Piston rings 9 are arranged in the zone 0.

While the invention has been described in detail with respect to a nowpreferred example and embodiment of the invention it will be understoodby those skilled in the art after understanding the invention thatvarious changes and modifications may be made without departing from thespirit and scope of the invention and it is intended, therefore, tocover all such changes and modifications in the appended claims.

What is claimed is:

1. In an internal combustion engine having a crosshead, the combinationwhich comprises a piston made substantially of light metal, said pistonhaving a main body portion and a skirt portion of greater diameter thansaid main body portion, a connecting rod for said piston having adifferent coeflicient of thermal expansion than said piston, and meansproviding an expansion compensating connection between said piston andsaid piston rod, said connection being positioned within said lesserdiameter main body portion of said piston preventing distortion of saidgreater diameter skirt portion by thermal expansion of said piston rod.

2. In an internal combustion engine having a crosshead, the combinationwhich comprises a piston made substantially of light metal and having amain body portion and a skirt portion of greater diameter than said mainbody portion, a piston rod having a different coeflicient of thermalexpansion. than said piston, connecting flange means at one end of saidpiston rod, a recess in said piston for receiving said flange means,said recess being positioned within said lesser diameter main bodyportion of said piston preventing distortion of said greater diameterskirt portion by thermal expansion with respect to said flange means,and means for connecting said piston rod flange means to said piston,said means being substantially wholly in said recess and maintaining arigid connection during said differing thermal expansions of said pistonand said piston rod.

3. In an internal combustion engine having a crosshead, the combinationwhich comprises a piston made substantially of light metal and having amain body portion and a skirt portion of greater diameter than said mainbody portion, piston rings around said main body portion of said piston,a steel piston rod having a sub stantially different coefiicient ofthermal expansion than said piston, a steel flange at one end of saidpiston rod, a recess in said main body portion of said piston andQwithin area of said piston rings, a plurality of bolts mal expansionsof said light metal piston and said steel piston rod. p,

References Cited in the file of this patent UNITED STATES PATENTS1,521,388 Pielstick Dec. 30, 1924 1,581,255 Watts Apr. 20, 19261,655,968 Maynard Jan. 10, 1928 1,909,004 Parsons, Sr. May 16, 1933Norton July7, 1936

